Hanuman Chalisa is a devotional song based on Lord Hanuman as the model devotee. The word "chālisā" is derived from "chālis" in Hindi, which means 40, as the Hanuman Chalisa has 40 verses.
The poem is called a chalisa as it contains forty (chalis in Hindi) verses. The structure of the poem is extremely simple and rhythmic, thus making it all the more popular. The poem praises Lord Hanuman’s strength and kindness and recounts the Lord’s great deeds.